Microwave tuner having sliding contactors

ABSTRACT

A microwave tuner having sliding electrical contactors is disclosed. The tuner includes a plunger structure movable within a hollow, evacuated microwave conductor, as of copper. The plunger includes a tungsten helix with the turns of the helix being fixedly secured near the leading edge of the plunger with the plane of the turns of the helix being generally parallel to the direction of movement of the plunger and with the trailing edge of the helix being free to move relative to the plunger. The loop formed by each turn of the helix has a generally oblong configuration with major and minor axes to be compressed between the opposed walls of the microwave conductive structure to be tuned, with the minor axes of the loops intersecting the walls to be contacted.

United States Patent [72] Inventor Robert C. Schmidt Woodside, Calif. [21] Appl. No. 19,602 [22] Filed Mar. 16, 1970 [45] Patented Oct. 19, 1971 [73] Assignee Varian Associates Palo Alto, Calif- [54] MICROWAVE TUNER HAVING SLIDING CONTACTORS 8 Claims, 5 Drawing Figs.

[52] US. Cl 315/553, 333/83 R, 315/546 [51] Int. Cl I10lj 23/20 [50] Field of Search 315/546, 5.47, 5.48, 5.53; 333/83 [56] References Cited UNITED STATES PATENTS 2,476,034 7/1949 Fox 333/83 X 2,487,078 11/1949 Sloan 315/546 X 2,742,617 4/1956 Bondley 2,829,352 4/l958 Hennies et al. 333/83 X 2,850,632 9/1958 Lyman et al. 333/83 X Primary Examiner-Herman Karl Saalbach Assistant ExaminerSaxfield Chatmon, Jr. Attarneys-Stanley Z. Cole and Gerald L. Moore ABSTRACT: A microwave tuner having sliding electrical contactors is disclosed. The tuner includes a plunger structure movable within a hollow, evacuated microwave conductor, as of copper. The plunger includes a tungsten helix with the turns of the helix being fixedly secured near the leading edge of the plunger with the plane of the turns of the helix being generally parallel to the direction of movement of the plunger and with the trailing edge of the helix being free to move relative to the plunger. The loop formed by each turn of the helix has a generally oblong configuration with major and minor axes to be compressed between the opposed walls of the microwave conductive structure to be tuned, with the minor axes of the loops intersecting the walls to be contacted.

DESCRIPTION OF THE PRIOR ART l-leretofore, cavity and waveguide tuners have been built which comprised a plunger structure having a forward lip portion projecting into an air-filled waveguide or cavity to be tuned. A conductive helix was mounted to the lip portion of the plunger with the turns of the helix passing through apertures in the lip of the-plunger. The turns of the helix were of larger diameter than theinside dimensions of the structure to be tuned such that the helix was compressed into firm engagement with the opposed walls of the structure to provide a radiofrequency short thereacross. The plunger was axially translatable within the microwave structure for moving the position of the short and, thus, for tuning same. Such a microwave tuner is disclosed and claimed in U.S. Pat. No. 2,829,352 issued Apr. 1, 1958 and assigned to the same assignee as the present invention.

While such a prior art tuner is suitable for operation in an air-filled waveguide or cavity at relatively low-power levels, such tuners are not well suited for use in tuning evacuated cavities of multicavity high-power klystron tubes which are gang tuned to certain predetermined preset channel frequencies. Such a multicavity klystron tube is disclosed and claimed in copending U.S. application Ser. No. 739,016 filed June 21, 1968 and assigned to the same assignee as the present invention.

In such gang-tuned multicavity klystrons, the tuners must be capable of being baked out with the body of the tube to rela-- tively high temperatures, such as 500 C, while the tube is being evacuated. After the bakcout, the tuner must function in a perfectly reliable manner without backlash and without mechanical hysteresis which would degrade the repeatability of the tuning.

Moreover, the tuner must be capable of operating to relatively high-power levels as of on the order of several kilowatts at C band.

SUMMARY OF THE PRESENT INVENTION The principle object of the present invention is the provision of an improved microwave tuner having sliding contactors.

One feature of the present invention is the provision of a tuning plunger movable within a hollow microwave conductor for tuning thereof, such tuning plungerhaving a plurality of resilient compressible electrically conductive loop portions with such loop portions being fixedly secured to the plunger at a peripheral portion of each loop which faces into the microwave structure and such loops being free to move relative to the plunger along a peripheral portion of each loop which faces out of the microwave structure, such loop portions being compressed against an inside wall of the microwave structure for making electrical contact between the plunger and the wall of the microwave structure for tuning same.

Another feature of the present invention is the same as the preceding feature including the provision of an electrically conductive member covering over the peripheral portion of the loops of the sliding contactor which face into the microwave structure, whereby such loop portions are shielded from the circulating radiofrequency currents within the tuned microwave structure.

Another feature of the present invention is the same as any one or more of the preceding features wherein the loop contactors are made of tungsten and that portion of the microwave structure contacted by the contactors being made of copper, and the microwave structure being evacuated, whereby the spring contactors do not gall the contacted surface of the microwave structure.

Other features and advantages of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic line diagram of a multicavity klystron incorporating features of the present invention,

FIG. 2 is an enlarged sectional view of a portion of the structure of FIG. 1 delineated by line 2-2 andtu med'90",

FIG. 3 is a sectional view of the structure FIG. 2 taken along line 33 in the direction of the arrows,

FIG. 4 is a sectional view of the structure of FIG. 3 taken along line 4-4 in the direction of the arrows, and

FIG. 5 is an enlarged detail view of an alternative embodiment to that portion of the structure of FIG. 3 delineated by line 5-5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. I, there is shown a multicavity klystron amplifier incorporating microwave tuners of the present invention. The klystron l is of the same basic configuration as that disclosed in the aforecited copending application Ser. No. 739,016. Briefly, the klystron 1 includes an electron gun assembly 2 for forming and projecting a beam of electrons 3 over an elongated beam 'path to a collector electrode 4 disposed at the terminal end of the beam 3. The electron gun 2 includes a thermionic cathode emitter 5 and a centrally apertured anode electrode 6. The anode 6 is operated at ground potential and the cathode 'emitter 5 is operated at a negative potential, as of several kilovolts, relative to ground via a power supply 7. i

A plurality of reentrant cavity resonators 8, 9, II and I2 are successively disposed along the beam path for successive electromagnetic interaction with the beam. Microwave energy to be amplified is applied to the input cavity 8 for exciting same and for velocity modulating the beam passable therethrough. Successive buncher cavities 9 and Il furthervelocity modulate the beam and the velocity modulation on the beam is converted into current density modulation in the drift region between cavities. The current density modulation on the beam excites the output cavity 12 and amplified microwave energy is extracted from the output cavity 12 via output coupling means 13 for transmission to a suitable utilization device such as an antenna, not shown.

The cavities 8, 9, I] and 12 are evacuated, in use, to a relatively low pressure as of IO" ton and a tuning plunger 14 is disposed in each of the resonators for tuning the operating frequency of the tube 1. Each tuning plunger 14 is operated by means of an actuating rod 15 which extends outwardly of the cavity resonator and which is sealed in a vacuumtight manner to the resonator via the intermediary of bellows 16, as of stainless steel. Ganged-tuning means, not shown, but described in detail in the aforecited copending application Ser. No. 739,016, serve to tune the various cavities in unison to any one of a number of predetermined channel frequencies. in a typical example, the klystron 1 produces several kilowatts of output microwave power at C-band.

During processing of the tube I, the tuners are baked out in place within the resonators to a typical temperature of 500 C. while the tube is being evacuated.

Referring now FIGS. 2-4 the tuning structure 14 will be described in greater detail. The cavity resonator I2 is formed by a section of hollow microwave conductor of a generally rectangular inside cross section, i.e., a section of rectangular waveguide having a pair of mutually opposed broad walls I8 and 19 interconnected by a pair of narrow sidewalls 21 and 22. The cavity 12 is closed at one end by a fixed closing wall 23 (see FIG. I) and the other end of the cavity is defined by the movable tuning plunger 14 which serves to provide a movable microwave short for determining the electrical length of the resonator and, thus, its resonant frequency. The region of the microwave conductor behind the movable plunger 14 is closed by end wall 24 which includes a central aperture 25 for passage of the actuating rod 15 therethrough. The bellows I6 is fixedly secured in a vacuumtight manner to the end wall at 26. The other end of the bellows 16 is sealed in a vacuumtight manner to the actuating rod 15 at 27.

The top and bottom walls 18 and 19 of the cavity are centrally apertured at 28 and 29 to allow for passage of the electron beam 3 therethrough. A pair of drift tube members 31 and 32 project from the broad walls reentrantly into the resonator 12 to define the electromagnetic interaction of the cavity 12.

The tuning plunger structure 14 includes a central main body portion or rod 33, as of copper. The main body portion 33 is elongated such as to extend substantially across the broad dimension of the cavity 12 and includes a pair of flats 34 and 35 formed on the sides of the rod 33 adjacent the broad walls 18 and 19 of the cavity 12. The leading and trailing edge of the rod 33 at 36 and 37, respectively, form cylindrical sections and each includes an array of peripheral grooves formed as portions of a helical groove cut into the periphery of the rod A helical tungsten wire 38, as of 0.007 inch diameter, is wound into the helical groove at 36 and 37. The turns of the helix form loops of generally oblong configuration having a major axis 39 and a minor axis 41 generally in the plane of the individual loops with the major axes 39 being generally parallel to the direction of movement of the plunger structure 14 and the minor axes 41 being generally perpendicular to the broad walls 18 and 19 of the cavity 12. The minor axes 41 are offset slightly, as by percent of the length of the major axis 39, to the rear of the center of the loops and the peripheral portion of the loop which intersects the minor axis 41 makes physical contact with the top and bottom broad walls 18 and 19, respectively, of the cavity 12. The loops of the helix are compressed to form an interference fit, such compression being within the range of 0.005 to 0.010 inches to provide firm engagement between contacting portions of the tungsten helix 38 and the broad walls 18 and 19, as of copper, of the cavity 12 The land portions of the grooves at the leading edge of the rod 33 at 36 are peened over the tungsten helical wire 38 to fixedly secure the helix to the rod 33 at the leading edge 36. However, at the trailing edge of the rod 33, the tungsten wire turns are freely slidable within the grooves at 37 to facilitate maintaining spring action of the helix in use.

The helix 38 is conveniently mounted to the rod 33 and fonned to the aforementioned oblong shape by starting with a cylindrical rod 33, cutting the helical groove into the rod, such groove having a relatively large number of turns per inch, such as 48 turns per inch. Flats 34 and 35 are then formed on opposite sides of the grooved rod 33 and provided with key slots 42 and 43, respectively, to receive aluminum inserts key to the slots 42 and 43 and having a triangular cross-sectional shape conforming to the space between the flats 34 and 35 and the tungsten wire 38. Tungsten wire 38 is then wound into the helical groove with a substantial amount of tension, such as one-half pound to three-quarters of a pound, such that the wire conforms to the shape of the inserts to provide the oblong shape for the loops of the helix. The land portions between adjacent grooves at the leading edge of the rod 36 are then peened over the wire 38 to fixedly secure the helix to the rod 33. The rod with helix mounted thereto is then placed in a chemical etch to etch out the aluminum inserts.

The plunger 14 includes a conductive yoke portion 45 as of monel which is fixedly secured to the rod portion 33 at the ends of the rod 33. A pair of sapphire bearings 46 are centrally mounted on the arms of the yoke 45 in alignment with the longitudinally axis of the rod 33. The yoke 45, wit bearings 46 in place, is dimensioned to provide a cold clearance of a few thousandths of an inch, such as 0.002 inches, between the bearings 46 and the inside narrow walls 21 and 22, respectively, of the cavity 12. The actuating rod 15, as of molybdenum, is fixedly secured to the central portion of the yoke 45, as by brazing.

A face plate 47, as of copper, is brazed over the leading edge of the plunger rod 33 and helix 38 to shunt the circulating microwave currents across the leading edge of the helix 38, thereby substantially improving the Q of the cavity 12 containing the tuning plunger 14. In a typical example at C bend, the face plate 47 has a height of 0.250 inches, a thickness of 0.060 inches, and a length.of 1.1 inches.

To facilitate cooling of the tuning plunger 14, in use, the yoke 45 may include a coolant passageway therein in fluid communication with a coolant passageway within the interior of the tuner actuating rod 15, such that coolant can be circulated through the actuating rod 15 and yoke 45.

Referring now to FIG. 5, there is shown an alternative embodiment of the present invention which is substantially the same as that depicted in FIGS. 2-4 with the exception that the trailing edge of the rod 33 extends and is brazed to the yoke 45 to facilitate cooling of the plunger in use. As in the embodiment of FIGS. 2-4 the tungsten helix 38 is freely slidable in the grooves at the trailing edge 37 of the rod portion 33 of the plunger 14.

Referring again to FIGS. 2-4, the top and bottom broad walls 18 and 19, respectively, of the cavity 12 are relieved at 49, as by 0.025 inches. This relieved portion 49 is out of the normal tuning range the tuning of the tuning plunger 14.

It is provided such that when the tube is being baked out at the elevated temperature of 500 C that the tuning plunger 14 can be retracted into the relieved portion to remove the compression on the helical spring contactors 38, such that the spring action of the helix is not annealed out of the helix at the bakeout temperature. After the bakeout, the plunger 14 is pushed inwardly of the cavity into the tuning range thereof.

Although the tuning plunger 14 has been shown as a pure inductive tuner, the tuning plunger may also include capacitive tuning arms projecting from the face plate 47 into the region of the interaction gap in the same manner as the capacitive tuning plates disclosed and claimed in U.S. Pat. No. 2,994,009 issued July 25, I961 and assigned to the same assignee as the present invention. Such capacitive tuning plates, movable in unison with the inductive plunger 14, served to substantially increase the tuning effect of the tuning plunger to extend the tuning range thereof.

In a typical example of the tuning plunger of FIGS. 2-4 a C- band klystron was tunable over an 8 percent bandwidth by a tuner movement of 0.200 inches.

The advantage of the tuning plunger in the present invention is that the resilient helix 38 provides electrical spring contactors which are devoid of mechanical hysteresis and backlash such that absolute repeatability of the tuning effect is obtained for certain positions of the tuner within the cavity 12. This absolute repeatability is essential for multichannel gangtuned tubes of the type disclosed in the aforecited copending application Ser. No. 739,0l6. The use of tungsten contactors 38 slidable upon a copper wall in an evacuated device is particularly useful since, in an evacuated device, tungsten is freely slidable upon copper and will not gall or seize thereon as do many other spring materials.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a tunable microwave apparatus a hollow microwave structure, a plunger structure movable within said hollow microwave structure for tuning said microwave structure, means carried from said plunger structure for making sliding electrical contact with the inside wall of said microwave structure, said contactor means including a plurality of resilient compressible electrically conductive loop portions disposed with the direction of movement of said movable plunger structure lying generally in the plane 'of said loop portions of said contactor means, means fixedly and rigidly attaching said loop portions of said contactor means to said plunger structure along a peripheral portion of each loop portion which is proximal to and disposed facing into said microwave structure, said loop portion being free to move relative to said plunger structure along a peripheral portion of each loop which faces out of said microwave structure and which is generally diametrically opposed to the region of said peripheral attachment of said loop portions to said plunger structure, and means for moving said plunger within said microwave structure for tuning of said microwave structure.

2. The apparatus of claim I wherein said loop portions of said contactor means are generally oblong-shaped having a major axis generally in the direction of movement of said plunger structure and a minor axis in the plane of the loop and perpendicular to the major axis, said contactor loop portions making electrically slidable contact with the inside wall of said microwave structure along diametrically opposed peripheral portions of each loop at the intersection of the minor axes with the periphery of said loop portions.

3. The apparatus of claim I wherein said plunger structure includes an electrically conductive portion which faces into the hollow microwave structure and which covers over the peripheral portion of said loop portions which face into said microwave structure,

4. The apparatus of claim 1 wherein said contactor means comprises a helix with each turn of the helix defining a loop portion of said contactor.

5. The apparatus of claim 1 wherein said microwave structure is evacuated, said resilient loop portions of said contactor means are made of tungsten, and the contacted inside wall of said microwave structures is made of copper.

6. The apparatus of claim 1 wherein said plunger structure includes an array of grooves with each groove lying generally in a plane of a respective one of said loop portions of said contactor means, and said peripheral portion of said loop portions which face away from the interior of said microwave structure being disposed in said grooves in freely slidable relation with respect to the sidewall of said grooves.

7. The apparatus of claim I wherein said microwave struc ture comprises a hollow conductor of generally rectangular inside section having a pair of opposed narrow walls, said plunger structure being of rectangular cross section to fit within and generally conform to the rectangular inside section of said microwave structure, said contactor loop portions lying generally in planes parallel to the planes of said narrow sidewalls and making electrical contact with said broad walls of said microwave structure, and wherein said means for moving said plunger structure within said microwave structure comprises an actuating rod, and said plunger structure including a yoke portion for affixing said plunger to said actuating rod.

8. The apparatus of claim 7 wherein said microwave structure comprises an evacuated cavity resonator, said broad walls of said microwave being apertured for passage of an electron beam therethrough for interaction with the electric fields of said cavity resonator. 

1. In a tunable microwave apparatus a hollow microwave structure, a plunger structure movable within said hollow microwave structure for tuning said microwave structure, means carried from said plunger structure for making sliding electrical contact with the inside wall of said microwave structure, said contactor means including a plurality of resilient compressible electrically conductive loop portions disposed with the direction of movement of said movable plunger structure lying generally in the plane of said loop portions of said contactor means, means fixedly and rigidly attaching said loop portions of said contactor means to said plunger structure along a peripheral portion of each loop portion which is proximal to and disposed facing into said microwave structure, said loop portion being free to move relative to said plunger structure along a peripheral portion of each loop which faces out of said microwave structure and which is generally diametrically opposed to the region of said peripheral attachment of said loop portions to said plunger structure, and means for moving said plunger within said microwave structure for tuning of said microwave structure.
 2. The apparatus of claim 1 wherein said loop portions of said contactor means are generally oblong-shaped having a major axis generally in the direction of movement of said plunger structure and a minor axis in the plane of the loop and perpendicular to the major axis, said contactor loop portions making electrically slidable contact with the inside wall of said microwave structure along diametrically opposed peripheral portions of each loop at the intersection of the minor axes with the periphery of said loop portions.
 3. The apparatus of claim 1 wherein said plunger structure includes an electrically conductive portion which faces into the hollow microwave structure and which covers over the peripheral portion of said loop portions which face into said microwave structure,
 4. The apparatus of claim 1 wherein said contactor means comprises a helix with each turn of the helix defining a loop portion of said contactor.
 5. The apparatus of claim 1 wherein said microwave structure is evacuated, said resilient loop portions of said contactor means are made of tungsten, and the contacted inside wall of said microwave structures is made of copper.
 6. The apparatus of claim 1 wherein said plunger structure includes an array of grooves with each groove lying generally in a plane of a respective one of said loop portions of said contactor means, and said peripheral portion of said loop portions which face away from the interior of said microwave structure being disposed in said grooves in freely slidable relation with respect to the sidewall of said grooves.
 7. The apparatus of claim 1 wherein said miCrowave structure comprises a hollow conductor of generally rectangular inside section having a pair of opposed narrow walls, said plunger structure being of rectangular cross section to fit within and generally conform to the rectangular inside section of said microwave structure, said contactor loop portions lying generally in planes parallel to the planes of said narrow sidewalls and making electrical contact with said broad walls of said microwave structure, and wherein said means for moving said plunger structure within said microwave structure comprises an actuating rod, and said plunger structure including a yoke portion for affixing said plunger to said actuating rod.
 8. The apparatus of claim 7 wherein said microwave structure comprises an evacuated cavity resonator, said broad walls of said microwave being apertured for passage of an electron beam therethrough for interaction with the electric fields of said cavity resonator. 